A conventional computed tomography (CT) scanner includes a rotating gantry rotatably mounted to a generally stationary gantry. The rotating gantry supports an x-ray tube and a detector array, which is mounted on the rotatable gantry opposite the x-ray tube, across an examination region. The rotating gantry and hence the x-ray tube and the detector array rotate around the examination region about a longitudinal or z-axis. The x-ray tube is configured to emit radiation that traverses the examination region (and a portion of a subject or object in the examination region) and illuminates the detector array. The detector array detects the radiation and generates electrical signals indicative of the examination region and the subject or object disposed therein. A reconstructor reconstructs the projection data, generating volumetric image data.
For spectral CT, the scanner may include an energy-resolving detector array such as a double-decker detector array. An example portion of a double-decker detector array 100 is shown in FIG. 1. The detector 100 includes a plurality of detector modules 102 aligned with respect to each other along a substrate 104 in an x-direction 106. Each module 102 includes first and second scintillator rows 108 and 110 optically coupled to corresponding first and second detection regions 112 and 114 of a photodiode substrate 116. The first and second scintillator rows 108 and 110 are arranged with respect to each other such that the first scintillator row 108 is above the second scintillator element 110 with respect to the incoming radiation 120. Generally, lower energy x-rays photons tend to be absorbed in the upper scintillator row 108 and higher energy x-ray photons tend to be absorbed in the lower scintillator row 110. The first and second scintillator rows 108 and 110 and the detection regions 112 and 114 extend along a z-direction 122, forming multiple rows of detector elements.
With the detector array 100 of FIG. 1, the resolution of the detector array 100 in the x-direction 106 generally is limited by a finite thickness 124 of the photodiode substrate 116 of each module 102 in the x-direction 106, which has been on the order of one hundred (100) microns to four hundred (400) microns. Unfortunately, thinner photodiode substrates are fragile and not well-suited for constructing detector modules such as the detector modules 102 of the detector array 100.